Dramatic growth in the amount of data that must be stored, combined with the need for faster, more reliable and more efficient data access and data management capabilities, have led many organizations to seek an improved way of storing, accessing and managing data. In traditional computer networks, each storage device is connected to only one server, and can be accessed only by that server. The computer protocol used to connect and transfer data between the server and storage device is called the small computer system interface, or SCSI. As more data must be stored and retrieved, organizations increasingly are finding that this one-to-one, or point-to-point, connection is not sufficiently fast, efficient and reliable to support growing demands for data access and storage. In addition, in most organizations today, data back-up—or creating a duplicate copy of data to protect it from corruption or loss—is accomplished by moving large volumes of stored data from a dedicated storage device over the primary computer network to a back-up storage device. Since the primary computer network also is responsible for conducting day-to-day computer operations, this added data movement results in substantial congestion, slowing all other computer operations.
Storage area networks, or SANs, which are computer networks dedicated to data storage, can help resolve some of these problems. A storage area network uses a different, higher-performance computer protocol, known as Fibre Channel, to transfer data. A storage area network also removes the one-to-one connection between servers and storage devices, and instead allows many servers to connect to and share access with many storage devices. The many-to-many connection enabled by the storage area network, combined with the Fibre Channel protocol, permits faster, more efficient, more reliable and more manageable data transfer processes. Furthermore, the storage area network, can be accomplished over data back-up operations, instead of over the primary computer network, thus substantially reducing congestion on the primary computer network and allowing much more efficient day-to-day operations.
Most storage devices in the market, however, continue to be sold with the small computer system interface. Additionally, most organizations have made significant investments in storage devices and servers that use the small computer system interface. Therefore, in order for devices of a Fibre Channel storage area network to function with storage devices that use SCSI, storage routers must be installed between these devices. In particular, storage routers are essential to shifting data back-up processes from a primary computer network to the storage area network, since most data back-up storage devices use the SCSI interface and can only connect to the storage area network through a storage router. As new computer protocols are introduced, storage routers will be increasingly essential to enable rapid, seamless communication among servers, storage devices and storage area network devices that use diverse protocols.
However, typical SANs are local Fibre Channel networks that serve one particular organization or one particular site. These SANs can be quite large, but cannot span great distances as they have distance limitations imposed upon them by the infrastructure necessary to carry Fibre Channel. For example, the Fibre Channel standard defines a means to communicate over spans up to 10 km and, in some cases, up to 30 km in length. In order to do this, however, the organization implementing the Fibre Channel network must typically own the fiber or lease dark fiber from some other party, which can be very expensive and, in most cases, is cost prohibitive.
This is because the fibers used to carry Fibre Channel traffic can carry only Fibre Channel protocol traffic. They cannot be shared with other protocols. It is therefore more cost effective to transmit data over long distances using a protocol that can be carried over already existing networks, such as those owned by phone companies that can carry ATM traffic, SONET traffic and IP traffic. Therefore, SANs are usually limited as to the geographic area that they can serve (i.e., they are limited to local operation). Furthermore, two or more geographically diverse SANs cannot inter-connect in a seamless fashion such that they operate and behave as if they were local to one another because the infrastructure to connect them does not exist or is cost prohibitive.
Related U.S. Patent Application entitled “Encapsulation Protocol for Linking Storage Area Networks Over a Packet Based Network” Serial No. 60/165,194, filed on Nov. 12, 1999, (the “Encapsulation” patent application) discloses an encapsulation protocol for linking storage area networks over a packet-based network that addresses the problems discussed above. The Encapsulation application is hereby incorporated by reference in its entirety. However, even with the solutions provided by the Encapsulation application, connecting two or more SANs together using an extender, such as the encapsulation protocol of the Encapsulation application, requires the addresses of SCSI devices from one SAN to be mapped to an intermediate address to get across the extender, and then to be mapped to another address on a remote SAN. This must be done in order for initiators (hosts) on one SAN to be able to address SCSI devices on a remote SAN as if they were SCSI devices on the local SAN to which the initiator is attached. These mappings should be done in a generic fashion so that different types of architectures (i.e., parallel BUS, Fibre Channel Protocol, etc.) containing SCSI devices can all be mapped using the same method.
Some solutions do exist for mapping the addressing of SCSI devices between two SANs, but these typically attempt to propagate the entire address of a SCSI device across the extender and re-use the same address on the remote SAN. For example, a parallel BUS SCSI device on a first SAN may have an address of BUS:0, target:1, and LUN (logical unit identifier):0. In prior art methods and systems, the extender propagates this information from the first SAN to a remote SAN, where the same address is used to identify the device on the remote SAN. This approach, however, has a twofold problem. One, it uses a method of address mapping that is limited to a single type of architecture, i.e., the method only provides for mapping a single type of SCSI architecture SCSI device (e.g., parallel BUS SCSI devices). Two, because the device address must be the same on both sides of the extender, there is no means to dynamically map SCSI devices across the extender.